The broad concept of utilizing controlled environments to promote storage life of perishable commodities such as fruits, meats, produce and grains is well known. Though the use of refrigeration units has been a common technique of preserving perishable goods, certain types of controlled atmosphere systems have recently been introduced which operate through the controlled manipulation of carbon dioxide and oxygen levels within transport/shipping containers in addition to the use of refrigeration. In this respect, hollow fiber permeable membranes are used for air separation in maintaining controlled carbon dioxide and oxygen levels within grain elevators and controlled atmosphere warehouses. As with most controlled atmosphere systems, those utilizing permeable membranes require a reliable source of compressed air. Typically, a compressor is used to provide a source of compressed air for the controlled atmosphere system. Additionally, since it is desirable to monitor the carbon dioxide and oxygen levels of the controlled atmosphere system, such systems typically include a sampling pump which is used to draw conditioned air from the transport/shipping container into carbon dioxide and oxygen sensing devices.
Recent advances in membrane technology have increased the efficiency and decreased the size of gas-permeable membrane systems thereby making the application of membrane technology more feasible for controlled atmosphere transport applications. However, though the technology associated with permeable membranes has advanced, transport refrigeration units typically do not include controlled atmosphere devices because of the reduced cargo space, increased weight, power and cost. Additionally, the corrosive marine environments and extreme temperature parameters typically encountered by mobile transport containers makes controlled atmosphere applications in conjunction with such containers very difficult.
One example of a prior art apparatus for producing a controlled atmosphere utilizing permeable membranes is disclosed in U.S. Pat. No. 4,187,391 issued to ROE. As disclosed therein, the ROE apparatus requires the use of a controller of high reliability. Existing prior art controllers have proven to be inadequate for such purposes because of the instability and reliability of the gas analysis components. Further, sampling pumps typically utilized to produce the necessary gas flow for these analyzers have also proven inadequate and expensive. Further, a processor employing complex logic to assign priorities to satisfy control parameters detect failure of the sensing components and default to a safe best mode operating condition under varying circumstances is required to insure produce life within the container. For mobile transport applications an additional problem encountered in shipping is that only limited electrical power is typically available for operating the system. The present invention specifically overcomes these and other deficiencies associated with prior art controlled atmospheric systems.